An NBC News poll shows that GOP presidential hopefuls Mitt Romney and Rick Santorum are neck-and-neck in Michigan, Romney's birthplace. Romney, meanwhile, has a comfortable lead in Arizona, which has a sizable Mormon population.

By Mark Murray, NBC News' Senior Political Editor

Less than a week before Tuesday’s crucial Republican presidential primary in Michigan, a new NBC News/Marist poll shows Mitt Romney and Rick Santorum locked in a statistical tie, while a separate NBC/Marist survey shows Romney comfortably leading in Arizona, which holds its primary the same day.

In Michigan – which has turned into a make-or-break contest for Romney – the former Massachusetts governor gets the support of 37 percent of likely GOP primary voters, including those who are leaning toward a particular candidate.

“Michigan is neck and neck,” says pollster Lee Miringoff, director of the Marist College Institute for Public Opinion, which conducted both surveys.

But in Arizona, Romney is on safer ground: He receives the support of 43 percent of likely GOP primary voters, Santorum gets 27 percent, Gingrich 16 percent and Paul 11 percent.

And looking ahead to November’s general election, President Barack Obama enjoys a double-digit edge over his closest GOP competition in Michigan (a state Republicans are hoping to target), while he’s trailing the leading Republicans in Arizona (which the Obama camp wants to put into play).

Romney vs. Santorum ideological breakdownIn both states, support for Romney and Santorum breaks down along ideological lines, as well as whether voters have already cast their ballots.

In Michigan, Santorum leads Romney among self-identified Tea Party supporters, 48 to 29 percent, and those who describe themselves as “very conservative,” 59 to 20 percent.

The same ideological pattern is true in Arizona, although Romney performs much better with the most conservative voters there than in Michigan.

And among those who have voted early or absentee in Arizona – more than half of all likely Republicans voters in the poll – Romney holds a 30-point advantage over Santorum, 52 to 22 percent.

Obama leads in Michigan, trails in ArizonaTurning to the general-election race in November, Obama leads Romney in Michigan by nearly 20 points among registered voters, 51 to 33 percent, with 15 percent undecided.

Against Paul, the president’s lead is 22 points (53 to 31 percent); against Santorum, it’s 26 points (55 to 29 percent); and against Gingrich, it’s 28 points (56 to 28 percent).

What’s more, 51 percent of registered Michigan voters approve of Obama’s job; 63 percent of them believe the auto industry bailout was a good idea (including 61 percent of independents and 42 percent of likely GOP primary voters); and a majority think the president deserves credit for the auto industry’s recovery.

But Arizona is tougher territory for the president, whose approval rating among registered voters in the state is just 38 percent.

In hypothetical match-ups, Obama trails Romney by five points (40 to 45 percent); Santorum by three (42 to 45 percent); Paul by 2 points (41 to 43 percent); yet he leads Gingrich by five (45 to 40 percent).